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GTC by Levanter

Been on my list for a while now.

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Levanter02/03/2018 18:14:29
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881 forum posts
436 photos

Fuselage sides and doublers net on the list. The copy of the plan I had made at the local print shop is fast reducing in size and big chunks came out when the sections of the fuselage were cut out and the short tail section stuck to the main body with drafting 3m drafting tape. Wherever possible components are made in pairs. Apart from the considerable tine saving it does ensure symmetry. It isn't generally the end of the world if some discrepancies creep in but at least any differences will be mirrored.
​In the usual way the paper template was stuck to one of two 2.5mm sheets (Grumpy is totally metric being of Spanish heritage) and the two sheet pinned together. Cutting closely to the line, it is an easy job to adjust to the finished size by light sanding.
​It was slightly different for the doublers because the plywood does not accept pins.

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​Here, the plan section is stuck to the top doubler blank and the two blanks were stuck together with 3m Spray Mount. This keeps the two parts securely held together through a variety of operations but is easily separated when required by slipping a steel rule into the joint and working them free. Any residue wipes of easily with white spirit (ordinary thinners).

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Here is a finished doubler. The angled slot on the left will take the plate for the wing bolts. The register on the bottom will take a support for the Rx tray and the two recesses in the cut-out on the right are for the servo rails. These make very secure anchorages for the internal components and guarantee accurate orientation.

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The 5mm longerons to run along the lower edges of the fuselage could not be persuaded to follow the curve at the nose so a little prior help was needed. The balsa sections were dampened slightly and given a pre-bend using these wedges. As the started to relax the wedges were pinched up to give progressively more curve. It was then left to fully dry for a couple of hours after which the longerons conformed with no further argument.

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The two fuselage side are now ready and the positions marked with a soft (B or 2B) so that only very light pressure is necessary to make a good line.
​Normally I follow Peter's advice and use contact adhesive for doublers which works very well. The downside for me is that I don't like glue on the balsa surface where there is fresh air for the cuts outs so carefully applying the glue to a line or masking up takes a bit of time. In this case because there are no wide areas I used aliphatic glue followed by weighting down. The glue face of the doubler was scored and criss-crossed using the rough side of a Permagrit. Plenty of weight is needed and it helps to put a suitable flat board under the weights to ensure even distribution.

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​Here are the finished formers for the front section. F2 has two rails near the bottom edge to take the front of the battery tray and this is the same height as the bottom edge of the lower cut-out in F2.
​The centrelines are clearly visible and the centre-pop marks as well.

p1040631.jpg

​These are the rear formers slimmed down as much as possible. The doubler on F8 will be fitted later as it will need to cater for the bevel of the rolled top of the fuselage.

​We are now ready to start assembly.

Levanter.

McG 696902/03/2018 18:31:28
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2622 forum posts
993 photos

Very neat build, Levanter.

And nice explanations as well. I like your provisioned "registers" to be able to position cross members or hardware more easily afterwards.

Perfecto yes

Cheers

Chris

Levanter02/03/2018 18:38:39
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881 forum posts
436 photos

Time to get the glue out. My favourite above everything else is aliphatic. I use epoxy only if there are compelling reasons why I can't use aliphatic. In some areas I use aliphatic with cyano assist but we will come on to that.

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I decant the aliphatic into small jam jars. The type used in hotels where one is not quite enough but two is too much. I never miss an opportunity to collect. I keep two small brushes in a small jar of water. Why two - well when I forget to put a brush back in the water and it goes semi hard I have a second ready to get me out of trouble. This happens often.

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​F5 being glued in place. F4 which is the same width is simply being used to support the weight parallel to the base so that it is stable while the glue sets. The notches were left to the last minute and were individually cut out to suit the longerons at each of the stations. Peter's plan is Imperial so I could not use the paper templates and anyway after fine tuning the fuselage edges after fitting the longerons some minor differences can easily be accounted for.

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​F4 being glued in place and now you can see I am being braver with the weights. The strip of balsa is acting like a shore on the base of the square keeping it properly aligned.

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​The three formers in the parallel section of the fuselage are now in place and this is to double check that they have all arrived at the same height. Any adjustments can be made by light sanding. It is good to check on accuracy at early stages and to keep doing so. I find errors have a nasty habit of accumulating so I try hard to correct things as I go along. Sometimes this takes much willpower (I am currently making my third dihedral brace!)

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​The other side is now glued in place and before placing the weights the alignment at the tail is check using the square end of a Permagrit. This is very important because if the two sides are not exactly on the same plane, when they are brought together for joining at the tail a twist will be induced. That is a problem very much better to avoid.
We are now ready to put the basic fuselage into the jig.

​Levanter

rgarde02/03/2018 21:32:34
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24 forum posts
17 photos

Nice to see that one of the GTC builds is making progress. You build very neatlyyes

Kind regards,

Richard

Levanter04/03/2018 10:34:58
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881 forum posts
436 photos

Now for a little bit if background on my fuselage jig. Space is my apartment is always at a premium so I try to be organised with my storage.

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​Here is my jig stored on the back of one of the built-in wardrobe doors. The doors are very sturdy and flat so ideal. The board sits on a rest with a shallow lip and the top is retained with a toggle like this:


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​Having worked a lot with sheet materials of many types I know only too well that boards simply stacked against a wall will end up with a bend over time. This way the board is held perfectly flat and out of the way. My main building board is kept on the other door likewise.

​The jig is instantly recognisable as the SLEC version. To ensure good adhesion of the sticky-backed vinyl the board was primed first with water based acrylic primer and then lightly sanded to remove any fluffy bits and raised grain. Another important thing with boards and laminates is that they are "balanced". IE if you do something to one side you should also do something to the other in order to avoid warping. Both sides were painted, one immediately after the other. The printed grid is useful but if I was to criticise anything I would have preferred the lines to be much finer and as I think mentioned elsewhere the plastic clamps are a bit flexible.

​I order extra clamps and many extra washers and was glad I did so.
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​The blind nuts are recessed on the underside of the board to retain a flat surface.
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​Which covered with cork tiles to give me another building board. It is a bit big for my normal use but very handy for the longer items.

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Apart from the lateral clamping points I also put a number on the centreline and these are extremely useful as I will show later.

​Levanter

Geoff Sleath04/03/2018 11:14:25
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3425 forum posts
295 photos

Like the 1 metre yacht rigs in the background. Mine are in a box tucked away in the workshop and the Graham Bantock designed Rhythm I built some years ago hasn't seen either water or even daylight for some years.

Your organised and tidy working area (as well as the building itself) puts me to shame!

Geoff

Levanter04/03/2018 11:34:46
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881 forum posts
436 photos

Geoff
​I would like boxes for mine but haven't got around to making any. Mine is a Topico and in dry dock as well at the moment. Might try and get back in commission for the summer.

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Mine is the red one, hard pressed with the medium rig. This was a regatta in Andratx harbour and the local club kindly let me join in informally before I got my registration, Just had to take the old sail numbers off. You should get yours back out on the water and have some fun. I will if you will!!

​Levanter

Geoff Sleath04/03/2018 12:01:48
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3425 forum posts
295 photos

You're very brave sailing in salt water. I always sailed on lakes and ponds with fresh water and it was impossible to keep things dry inside the hull, especially in a bit of a blow as in your picture. Most of us sailed using 27Mhz 2 channel systems and had to keep a stock of crystals to avoid clashes.

I'm guessing Andratx is the one in the SW corner of Mallorca? I first visited riding our tandem solo because my wife was tired after our flight. We were staying in a small hotel in the next bay to the east (can't recall the name) and I had a short ride solo over the hill into Andatx. It was a long time ago when I was both young and as fit as a butcher's cat

Geoff

Levanter04/03/2018 12:07:02
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881 forum posts
436 photos

Now to put the fuselage jig to work.

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Here the nose is in the jig and it is quite a tight bend between F1 and F2. There was a bit of creaking going on so I put some razor saw cuts in the longerons while gently moving the clamps closer together. This stopped the protesting and we managed to get the sides touching F1 without a mishap. To help take the strain of the join onto F1 you can see two strips of balsa glued to the top and bottom edges. The bottom one was kept in place until most of the bottom sheeting was in place. The top had to be removed before starting planking but by then there was very little strain.

p1040643.jpg

​Another view of the jig in use with loads of rubber bands to hold the tops of the clamps together. In a way this is quite useful as you can adjust the amount of pressure by adding bands until the joints are fully closed. Incidentally the rubber bands are kept in an old chocolate tin. This keeps the light out which is enemy number one for rubber. The bands are now in their fourth year and all perfect except those that I gave an unfair amount of stretching.

​The sides of the fuselage behind F5 are basically a straight taper that needs very little force to close. The only thing is to be careful to keep the sides equally spaced and here, the centrelines left on the formers can be projected down onto the printed centreline to ensure all is how it should be. This is where I would have liked the printed lines to be finer for example.

Levanter

Levanter04/03/2018 12:13:39
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881 forum posts
436 photos

Hi Geoff
​You are spot on and I reckon the place you stayed at was probably Camp de Mar or possibly Paguera. Either way I know those hills so yes, you must have been seriously fit. My cycling exploits are confined to the flat track between Port D'Andratx and the town of Andratx.
​Yes, the salt water did require some aftercare but the waves are fun along with the full sized stuff and of course the ducks!

Levanter05/03/2018 10:28:51
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881 forum posts
436 photos

Going back to the centreline fixing points on the jig they serve two very useful functions. Firstly they can provide a positive stop to locate the fuselage longitudinally. If I now want to take the model off the jig for any reason I can put is back knowing that it is relocating in exactly the right place.

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​This is actually a picture of the tail end of Toot Sweet. Another Peter Miller design and a the most recent completion. At the far right of the picture you can see a temporary post. Later this will be removed to make way for the post of the fin. The temporary post is chamfered evenly and this chamfer locate in the slot of the SLEC clamps. It is made from the same stock as the fin post to ensure compatibility.


p1280674.jpg

As can just be seen on the extreme right of the above photo. This makes it very easy to make sure the rear sides of the fuselage are brought together exactly on the centreline but additionally it makes sure that the tail and hence the slot for the fin is truly vertical.

​I can now be sure that the fuselage is not twisted and that the fin will slot into place without needing any further adjustment.

​This is also a convenient time to make sure the tailplane seat is level. My favourite method here is to put a straight edge across the seat. The straight edge should be at least as wide as the jig board for best accuracy and then the measurements from the straight edge to the board should be the same both sides. Any minor discrepancy can be sanded out but more often that not, no trimming is necessary provided the previous steps are kept nice and tidy. I don't use a spirit level ever since finding out my table top was not that flat.

Levanter

Levanter08/03/2018 11:33:49
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881 forum posts
436 photos

More work on the fuselage to prepare it for the planking over the nose and the rolled sheet decking. I have made the decking a bit higher than shown on the plan so F5b is correspondingly taller. The angle of the former is slightly arbitrary but I suppose a taper is necessary so that the wing releases itself if the bolts get sheared in an angry moment. If the former remained vertical I imagine the wing would jam causing damage to itself and perhaps the fuselage as well.

p1040645.jpg

Anyway the angle was taken from the plan using this adjustable bevel / protractor.


p1040646.jpg

​And transferred to a scrap of balsa used as a jig to give the angled former something to lean on while the glue dries.

p1040647.jpg

​The jig was tacked to the lower part of F5 with two tiny spots of glue and stayed in place until the angled former F5b was securely glued.

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After which is as snapped off hardly leaving a mark.

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F1 was fitted with a 5mm doubler (not on the plan). This was for two reasons:
​First it secures the ends of the fuselage sides which are only glued to the edge of a 2.5mm former.
​Second, it provides a wider bearing surface for the forward end of the planks. F3 at the rear end of the planking is shown with a doubler. Here you can clearly see the saw cuts in the longerons to help them negotiate the curve immediately behind the spinner,

p1040657.jpg

THis was also a good time to bore the holes for the snakes and fitting them before closing the fuselage with the rolled sheeting. The cross grained lower sheeting was already in place as this does help keep the fuselage in good shape.

​Levanter​

Tim Ballinger08/03/2018 16:43:39
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554 forum posts
229 photos

Looking a real tidy build. I doubled up on F1 as well for the same reason .

Tim

Levanter09/03/2018 09:48:14
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881 forum posts
436 photos

No to the planking of the nose. I stuck to Peter's 1/4" planks (6mm for me) but the top of the fuselage side has quite a pronounced curve which I did not want to have to follow for the whole planking process. In a similar way to the garboard plank on a boat which is generally wider than the others and a strange shape.

p1040662.jpg

This the first plank in place and is wide at both ends and narrow in the middle. This allows me to use more regular shaped planks for the remainder of the job. Because the plank is wider than normal the back was hollowed out slightly with my curved Permagrit to sit tightly on the curve of the formers. As the remaining planks are quite narrow is not really essential to hollow the backs so I didn't. The shape can be seen quite clearly on the plank lying on the towel.

p1040663.jpg

More planks in place working from the top on boat sides simultaneously. The risk of distortion using balsa planks that require little force to bring them into place is very low. In boatbuilding with harder planks it is important. Anyway it is good practice. The masking tape was useful to hold the planks in good edge contact while the glue was drying.

p1040664.jpg

Another view where you can see that each plank is tapered so that each one takes a share in forming the compound curve. It may help to think about the construction of a wooden barrel where each stave is tapered at both ends. The stave are also bevelled so that the edges of the planks have a nice uniform joint. The actual geometry is slightly more complicated because the tapers are not straight lines but slightly curved. In practice this is not too hard to do at this scale by eye. In larger scale and full size the curves would be plotted and marked out.
p1040669.jpg

​Nearly done and this is the closing plank and very satisfying to fit. The tapers and the slight curve are evident.
​In planking terms the shape of Grumpy's nose is not extreme and it was very easy to make all the planks run full length. There are no inserts or wedges. Again it helps to think of a barrel which being "barrel" shaped of course is wider in the middle than at the ends. Therefor the circumference is longer in the middle than at the ends. It follows that if all the staves (planks) are continuous the planks have to be narrower at the ends as they have less distance to make up. The analogy is very close and very useful.

p1040670.jpg

Planking complete. There are no gaps and therefore no filler required. Also the glue lines are as thin as possible so sanding is easy. The shape is quite uniform so a minimum of sanding is necessary to get a completely smooth surface.

Levanter

Ron Gray09/03/2018 10:40:19
1480 forum posts
363 photos

Nice work! I'm afraid mine is still at the planning stage but I have taken delivery of the 2 ASP 30's for it so can finalise the nacelles now - already seen that as these engines are really compact, I have more room than I thought!

McG 696909/03/2018 10:49:56
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2622 forum posts
993 photos

Hi Levanter,

It's quite obvious that you really enjoy 'planking'.

Maybe one day, I'll make a small - 'rescue' type - boat model as well, just to see if I would enjoy planking. question

Very neat 'nose' you have there, young man. yes

Cheers

Chris

Levanter09/03/2018 11:09:29
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881 forum posts
436 photos

Thanks you for the commentaries above and before.

​Are you fitting four strokes Ron or are you scaling up with two strokes. I have seen mixed reports whether it is wise to invert four strokes and there are many doomsayers who would say a twin IC aircraft is asking for trouble. I am taking Peters reassurance from Peter that all will be fine.

I like inverted because of the clean lines but I have always checked to make sure the cylinder head will not be the first point of contact in a nose over. It was marginal on Oodalally so I am fitting slightly larger wheels to get more clearance.

​I like planking Chris and this is a small job. On bigger jobs that can take days it pays to have a diversionary task because it can become a bit tedious. There are only 17 planks on Grumpy. As it happens I have a particular liking for doing caps strips, good food, good wine and good company.

Levanter

Geoff Sleath09/03/2018 11:57:23
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3425 forum posts
295 photos

Planking can be quite satisfying but this is the only model I've had to do a lot of:

veronica hull 6.jpg

It's my 45" Thames sailing barge hull. Most of it is flat sided but the bow and stern needed a bit of planking. Being an aeromodeller it's mostly glassed 3mm balsa. The hull is more or less complete but it's been stalled for a couple of years whilst I get the courage to do the rigging and 5 sails!

As regards engines, I don't think there's a great problem using 4 strokes inverted provided you get the fuel tank height right to avoid fuel syphoning. However with a twin it would be electric all the way for me I'm afraid. Especially one this size. Never the less, with your fine building there shouldn't be a problem however you choose to go.

Geoff

Biggles' Elder Brother - Moderator09/03/2018 12:09:36
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Moderator
15748 forum posts
1460 photos

Nice work Levanter - following with interest.

BEB

Levanter11/03/2018 11:13:50
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881 forum posts
436 photos

Some more work on the fuselage which turns to the rolled sheet decking at the rear. First job was to fix the small extra former F8a on the fore side of F8 to locate the spine. The spine is then securely held at the without interfering with the slot that will later take the vertical fin.

p1040665.jpg

​Here I do it the other way round from the instructions by starting at the top. The reason for this is the curve is most severe at the top so making this the closing joint has proved difficult to make neat on previous builds.
​Here the starboard side is being fixed to the spine with plenty of spare material to trim back against the slanting F5a (Yes I have made that mistake before!).
​The centreline was marked on the top of the spine and the port side masked with a run of tape. This makes it much easier to get the glue on quickly on the working side of the spine. Later the port side will need to be glued to the other side of the spine and it is unhelpful for the wood to be already smeared with glue or have blobs where the glue has squeezed out.
​The pins at the front and rear are simply to make a quick register to stop the sheeting sliding around and taking more than its fair share of the spine. The strip of wood is packing to stop the clamps digging into the decking surface.
p1040667.jpg

Here is a similar view without the clutter of the clamps. The glue line for the port sheeting is nice and clean.
​The wing clamping plate does not have blind nuts. The plate is made from high quality ply with many thin layers and on the underside doublers can just be seen to give a generous length of thread. The ply itself is drilled and tapped and the threads then hardened with cyano. The tap was then run through again to take out any furry bits and to true up the thread form. This will produce ample strength for the nylon wing bolts.

p1040843.jpg

​The tight curve at the top of the decking shows up very clearly. Here the port side has nearly been cajoled into place. The masking tape is used to induce the curve while the dampened balsa creeps around. It probably took three or four stages to get the curve fully developed but this was one by damping the sheeting with water. No ammonia was used and I have never needed to. The trick is to only damp the balsa in narrow strips where the bend is required. If the whole sheet is damp is becomes floppy and it will not wrap where wanted.
​The decking blanks were cut leaving a small trimming allowance so sand off at the joins with the existing fuselage sides.

p1050007.jpg

Back to the fore end and the sheeting conforms closely to the former F5a but in particular the top is nice and fair.

​Also in this photo is the packing block fitted to the wing plate and the holes line with thin walled aluminium tube. This prevents the edges of holes being "drawn" by the flexible nylon bolts if the wing tips get caught. The tube also acts as a sheer point so that in the event of hard impact the bolts will be encouraged to break cleanly at this point rather than stretch and pull causing unwanted damage to the woodwork.

Levanter



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